Microsoft's share of the operating system market dipped below 90 percent for the first time during November with Windows accounting for 89.6 percent of computers accessing the web, according to Net Applications.

The research firm, which monitors 40,000 websites to establish market share and trends, said the figure marked a 0.84 percent drop from October - the largest Windows market share decline since 2006.

Windows market shareApple's Mac OS X was the biggest beneficiary of Windows' decline, achieving 8.9 percent of the market by the end of November. Net Applications said Apple's OS has now accounted for more than 8 percent of the market for three months in a row.

However, Vince Vizzaccarro, Net Applications' executive vice president of marketing, said that a higher-than-average number of weekends in November may have been a contributory factor, given that Windows' share of the market typically drops once the working week is up.

"The more home users who are online, using Macs and Firefox and Safari, the more those shares go up," he said.

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With additional reporting from Computerworld US